Download THE ENDROCINE SYSTEM

THE ENDROCINE SYSTEM
ENDOCRINE ORGANS
AN OVERVIEW
• Endocrine glands are ductless glands that
produce and release hormones to the blood
through diffusion
• Endocrine glands may be strictly endocrine,
such as the pituitary, thyroid, parathyroid,
adrenal, pineal and thymus; or they may be
organs that have hormone production as one of
many functions, such as the pancreas, gonads,
hypothalamus, and others
HORMONES
• Chemistry of Hormones
– Hormones are long-distance chemical signals
that are secreted by the cells to the
extracellular fluid and regulate the metabolic
functions of other cells
– Most hormones are amino acid bases, but
gonadal and adrenocortical hormones are
steroids, derived from cholesterol
HORMONES
• Mechanisms of Hormone Action
– Hormones typically produce changes in membrane
permeability or potential, stimulate synthesis of
proteins or regulatory molecules, activate or
deactivate enzymes, induce secretory activity, or
stimulate mitosis
– Nearly all amino acid-based hormones exert their
effects through an intracellular second messenger
that is activated when a hormone binds to a
membrane receptor
– Steroid hormones are lipid soluble and diffuse into the
cell, where they bind to intracellular receptors,
migrate to the nucleus, and activate specific target
sequences of DNA
Second-messenger mechanisms of
Amino Acid-Based Hormones
Second-messenger mechanisms of
Amino Acid-Based Hormones
Direct Gene Activation Mechanism
of Steroid Hormones
HORMONES
• Target Cell Specificity
– Cells must have specific membrane or intracellular
receptors to which hormones can bind
– Target cell response depends on three factors: blood
levels of the hormone, relative numbers of target cell
receptors, and affinity of the receptor for the hormone
– Target cells can change their sensitivity to a hormone
by changing the number of receptors
HORMONES
• Half-Life, Onset, and Duration of Hormone
Activity
– The concentration of a hormone reflects its
rate of release, and the rate of inactivation
and removal from the body
– The half-life of a hormone is the duration of
time a hormone remains in the blood, and is
shortest for water-soluble hormones
– Target organ response and duration of
response vary widely among hormones
HORMONES
• Interaction of Hormones at Target Cells
– Permissiveness occurs when one hormone
cannot exert its full effect without another
hormone being present
– Synergism occurs when more than one
hormone produces the same effects in a
target cell, and their combined effects are
amplified
– Antagonism occurs when one hormone
opposes the action of another hormone
HORMONES
• Control of Hormone Release
– Most hormone synthesis and release is
regulated through negative feedback
mechanisms
– Endocrine gland stimuli may be humoral,
neural, or hormonal
– Nervous system modulation allows hormone
secretion to be modified by the nervous
stimulation in response to changing body
needs
Three Different Mechanisms of
Endocrine Gland Stimuli
ENDOCRINE ORGANS
MAJOR ENDOCRINE ORGANS
• The Pituitary Gland (Hypophysis)
– The pituitary gland is connected to the hypothalamus via a stalk, the
infundibulum, and consists of two lobes: the anterior pituitary, or
adenohypophysis, and the posterior pituitary, or neurohypophysis
– There are six adenohypophyseal hormones and one prohormone
• Growth hormone (GH) stimulates body cells to increase in size and divide
• Thyroid stimulating hormone TSH) is a tropic hormone that stimulates
normal development and secretion of the thyroid gland
• Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to
release corticosteroid hormones
• Follicle-stimulating hormone (FSH) stimulates gamete production
• Leutinizing hormone (LH) promotes ovulation in females and production of
gonadal hormones
• Prolactin stimulates milk production in females, and may enhance
testosterone in males
• Pro-opiomelanocortin (POMC) is a prohormone that is the source of
adrenocorticotropic hormone and two opiates
MAJOR ENDOCRINE ORGANS
• The Pituitary Gland (Hypophysis)
– Two neurohormones are synthesized by the
hypothalamus and secreted by the posterior
pituitary
• Oxytocin acts on the smooth muscle of the uterus
and breast to cause uterine contractions during
childbirth and milk let-down during nursing
• Antidiuretic hormone (ADH) acts on kidney tubules
to promote increased water reabsorption
PITUITARY GLAND
GROWTH HORMONES
MAJOR ENDOCRINE ORGANS
• The Thyroid Gland
– The thyroid gland consists of hollow follicles with
follicle cells that produce thyroglobulin, and
parafollicular cells that produce calcitonin
– Thyroid hormone consists of two amine hormones:
thyroxine (T4) and triiodothyronine (T3), that act on all
body cells to increase basal metabolic rate and body
heat production
– Calcitonin is a peptide hormone that lowers blood
calcium by inhibiting osteoclast activity, and
stimulates Ca2+ uptake and incorporation into the
bone matrix
THYROID GLAND
THYROID HORMONES
THYROID DISORDERS
MAJOR ENDOCRINE ORGANS
• The Parathyroid Gland
– The parathyroid glands contain chief cells that
secrete parathyroid hormone , or
parathormone
PARATHYROID GLAND
PARATHYROID HORMONES
EFFECTS
MAJOR ENDOCRINE ORGANS
• The Adrenal (Suprarenal) Glands
– The adrenal glands, or suprarenal glands, consist of two regions:
an inner adrenal medulla and an outer adrenal cortex
– The adrenal cortex produces corticosteroids from three distinct
regions: the zona glomerulosa, the zona fasciculata, and the
zona reticularis
• Mineralocorticoids, mostly aldosterone, are essential to regulation of
electrolyte concentrations of extracellular fluids
• Aldosterone secretion is regulated by the renin-angiotensin
mechanism, fluctuating blood concentrations of sodium and
potassium ions, and secretion of ACTH
• Glucocorticoids are released in response to stress through the
action of ACTH
• Gonadocorticoids are mostly weak androgens, which are converted
to testosterone and estrogen in the tissue cells
– The adrenal medulla contains chromaffin cells that synthesize
epinephrine and norepinephrine
ADRENAL GLAND
ALDOSTERONE
CUSHING’S DISEASE
STRESS
and
THE ADRENAL GLAND
MAJOR ENDOCRINE ORGANS
• The Pancreas
– The pancreas is a mixed gland that contains
both endocrine and exocrine gland cells
• Glucagon targets the liver where it promotes
glycogenolysis, gluconeogenesis, and release of
glucose to the blood
• Insulin lowers blood sugar levels by enhancing
membrane transport of glucose into body cells
PANCREAS
REGULATION OF BLOOD SUGAR
LEVELS
SYMPTOMATIC RESULTS OF INSULIN DEFICIT
(DIABETES MELLITUS)
MAJOR ENDOCRINE ORGANS
• The Gonads
– The ovaries produce estrogens and progesterone
– The testes produce testosterone
• The Pineal Gland
– Secrets melatonin, a hormone derived from serotonin, in a
diurnal cycle
– Indirectly receives input from the visual pathways in order to
determine the timing of day and night
• The Thymus
– The thymus produces thymopoietin, thymic factor, and thymosin,
which are essential for the development of T lymphocytes and
the immune response
ENDOCRINE ORGANS
OTHER HORMONE-PRODUCING
STRUCTURES
• The atria of the heart contain specialized cells that secrete atria
natriuretic factor resulting in decreased blood volume, blood
pressure, and blood sodium concentration
• The gastrointestinal tract contains enteroendocrine cells throughout
the mucosa that secrete hormones to regulate digestive functions
• The placenta secretes estrogens, progesterone, and human
chorionic gonadotropin, which act on the uterus to influence
pregnancy
• The kidneys produce erythropoietin, which signals the bone marrow
to produce red blood cells
• The skin produces cholecalciferol, an inactive form of vitamin D3
• Adipose tissue produces leptin, which acts on the CNS to produce a
feeling of satiety, and resistin, an insulin antagonist
DEVELOPMENTAL ASPECTS
OF
THE ENDOCRINE SYSTEM
• Endocrine glands derived from mesoderm
produce steroid hormones; those derived from
ectoderm or endoderm produce amines,
peptides, or protein hormones
• Environmental pollutants have been
demonstrated to have effects on sex hormones,
thyroid hormone, and glucocorticoids
• Old age may bring about changes in rate of
hormone secretion, breakdown, excretion, and
target cell sensitivity